Medical sensor for reducing motion artifacts and technique for using the same

ABSTRACT

A sensor for pulse oximetry or other applications utilizing spectrophotometry may be adapted to reduce motion artifacts by fixing the optical distance between an emitter and detector. A flexible sensor is provided with a stiffening member to hold the emitter and detector of the sensor in a relatively fixed position when applied to a patient. Further, an annular or partially annular sensor is adapted to hold an emitter and detector of the sensor in a relatively fixed position when applied to a patient. A clip-style sensor is provided with a spacer that controls the distance between the emitter and detector.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation of U.S. application Ser. No.11/241,375 filed Sep. 29, 2005, the disclosure of which is herebyincorporated by reference in its entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates generally to medical devices and, moreparticularly, to sensors used for sensing physiological parameters of apatient.

2. Description of the Related Art

This section is intended to introduce the reader to various aspects ofart that may be related to various aspects of the present invention,which are described and/or claimed below. This discussion is believed tobe helpful in providing the reader with background information tofacilitate a better understanding of the various aspects of the presentinvention. Accordingly, it should be understood that these statementsare to be read in this light, and not as admissions of prior art.

In the field of medicine, doctors often desire to monitor certainphysiological characteristics of their patients. Accordingly, a widevariety of devices have been developed for monitoring many suchcharacteristics of a patient. Such devices provide doctors and otherhealthcare personnel with the information they need to provide the bestpossible healthcare for their patients. As a result, such monitoringdevices have become an indispensable part of modern medicine.

One technique for monitoring certain physiological characteristics of apatient is commonly referred to as pulse oximetry, and the devices builtbased upon pulse oximetry techniques are commonly referred to as pulseoximeters. Pulse oximetry may be used to measure various blood flowcharacteristics, such as the blood-oxygen saturation of hemoglobin inarterial blood, the volume of individual blood pulsations supplying thetissue, and/or the rate of blood pulsations corresponding to eachheartbeat of a patient. In fact, the “pulse” in pulse oximetry refers tothe time varying amount of arterial blood in the tissue during eachcardiac cycle.

Pulse oximeters typically utilize a non-invasive sensor that transmitselectromagnetic radiation, such as light, through a patient's tissue andthat photoelectrically detects the absorption and scattering of thetransmitted light in such tissue. One or more of the above physiologicalcharacteristics may then be calculated based upon the amount of lightabsorbed and scattered. More specifically, the light passed through thetissue is typically selected to be of one or more wavelengths that maybe absorbed and scattered by the blood in an amount correlative to theamount of the blood constituent present in the tissue. The measuredamount of light absorbed and scattered may then be used to estimate theamount of blood constituent in the tissue using various algorithms.

Pulse oximetry readings measure the pulsatile, dynamic changes in amountand type of blood constituents in tissue. Other events besides thepulsing of arterial blood may lead to modulation of the light path,direction, and the amount of light detected by the sensor, creatingerror in these measurements. Pulse oximetry is sensitive to movement,and various types of motion may cause artifacts that may obscure theblood constituent signal. For example, motion artifacts may be caused bymoving a sensor in relation to the tissue, by increasing or decreasingthe physical distance between emitters and detectors in a sensor, bychanging the direction of emitters or detectors with respect to tissueor each other, by changing the angles of incidence and interfaces probedby the light, by directing the optical path through different amounts ortypes of tissue, or by expanding, compressing or otherwise alteringtissue near a sensor. In the emergency room, critical care, intensivecare, and trauma center settings, where pulse oximetry is commonly usedfor patient monitoring, the wide variety of sources of motion artifactsincludes moving of a patient or the sensor by healthcare workers,physical motion of an unanaesthetised or ambulatory patient, shivering,seizures, agitation, response to pain and loss of neural control. Thesemotions oftentimes have similar frequency content to the pulse, and maylead to similar or even larger optical modulations than the pulse.

Two categories of pulse oximetry sensors in common use may be classifiedby their pattern of use: the disposable and the reusable sensor.Disposable sensors are typically flexible bandage-type structures thatmay be attached to the patient with adhesive materials, providing acontact between the patient's skin and the sensor components. Disposablesensors have multiple advantages, including ease of conformation to thepatient. The flexible nature of disposable sensors further renders themsusceptible to motion artifacts caused by mechanical deformation of thesensor, which changes the amount of light detected. Reusable sensors,often semi-rigid or rigid clip-type devices, are also vulnerable tomotion artifacts, such as artifacts caused by partial opening of theclip in response to patient motion. Both categories of sensors may havemodulations of detected light induced by the physical motion of thesensor components with respect to each other and the tissue.

Motion artifacts may sometimes be addressed by signal processing andfiltering to mitigate the effects of motion after the motion hasoccurred. However, it would be desirable to provide a sensor thatreduces the occurrence of movement that may lead to motion artifacts.

SUMMARY

Certain aspects commensurate in scope with the originally claimedinvention are set forth below. It should be understood that theseaspects are presented merely to provide the reader with a brief summaryof certain forms of the invention might take and that these aspects arenot intended to limit the scope of the invention. Indeed, the inventionmay encompass a variety of aspects that may not be set forth below.

There is provided a sensor that includes a sensor body, and an emitterand a detector disposed on the sensor body. The sensor body is adaptedto hold the emitter and detector at a substantially fixed opticaldistance relative to one another when the sensor is applied to apatient.

There is also provided a pulse oximetry system that includes a pulseoximetry monitor and a pulse oximetry sensor adapted to be operativelycoupled to the monitor. The sensor includes a sensor body, and anemitter and a detector disposed on the sensor body. The sensor body isadapted to hold the emitter and detector at a substantially fixedoptical distance relative to one another when the sensor is applied to apatient.

There is also provided a method of operating a sensor that includesfixing the optical distance between an emitter and a detector relativeto one another, whereby the emitter and the detector are disposed on asensor body.

There is also provided a method of manufacturing a sensor that includesproviding a sensor body on which an emitter and a detector are disposed,whereby the sensor body is adapted to hold the emitter and the detectorat a fixed optical distance.

BRIEF DESCRIPTION OF THE DRAWINGS

Advantages of the invention may become apparent upon reading thefollowing detailed description and upon reference to the drawings inwhich:

FIG. 1 illustrates a perspective view of an exemplary bandage-stylepulse oximetry sensor with a stiffening member on the tissue-contactingside of the sensor body;

FIG. 2 illustrates a perspective view of an exemplary bandage-stylepulse oximetry sensor with a brass stiffening member applied to thesurface of the sensor body that does not contact a patient's tissueduring normal use;

FIG. 3A illustrates a view showing the interior of an exemplarybandage-style pulse oximetry sensor with an embedded stiffening member;

FIG. 3B illustrates a perspective view of an exemplary bandage-stylepulse oximetry sensor with an embedded, removable stiffening member;

FIG. 4A illustrates a view showing the interior of an exemplaryreflectance bandage-style pulse oximetry sensor with an embeddedstiffening member including a rigid portion that surrounds the emitterand the detector and a flexible portion;

FIG. 4B illustrates a view showing an exemplary reflectancebandage-style pulse oximetry sensor with a stiffening member surroundingthe emitter and detector;

FIG. 4C illustrates a perspective view of an exemplary reflectancebandage-style pulse oximetry sensor with a rigid portion that surroundsthe emitter and the detector and an embedded, removable stiffeningmember that is flexible;

FIG. 5A illustrates a perspective view of an exemplary bandage-stylepulse oximetry sensor with a fluid-filled chamber;

FIG. 5B illustrates a perspective view of the pulse oximetry sensor ofFIG. 5A in which the fluid-filled chamber includes a valve;

FIG. 6 illustrates a perspective view of an exemplary bandage-stylepulse oximetry sensor with two fluid-filled chambers separated by abreakable barrier;

FIG. 7 illustrates a perspective view of an exemplary pulse oximetrysensor according to the present invention with a removable rigid sleeve;

FIG. 8A illustrates a perspective view of an exemplary annular pulseoximetry sensor according to the present invention;

FIG. 8B illustrates a perspective view of the pulse oximetry sensor ofFIG. 8A with an adjustment strap;

FIG. 9 illustrates an embodiment of an exemplary partially annular pulseoximetry sensor according to the present invention;

FIG. 10 illustrates a cross-sectional view of an exemplary clip-stylepulse oximetry sensor with a spacer that moves to adjust the distancebetween the two portions of the clip;

FIG. 11A illustrates a cross-sectional view of an exemplary clip-stylepulse oximetry sensor with a removable spacer according to the presentinvention;

FIG. 11B is a perspective view of the removable spacer of FIG. 11A;

FIG. 12 illustrates a perspective view of an exemplary clip-style pulseoximetry sensor in which the two portions of the clip are adjusted witha sliding pin; and

FIG. 13 illustrates a pulse oximetry system coupled to a multi-parameterpatient monitor and a sensor according to embodiments of the presentinvention.

DETAILED DESCRIPTION OF SPECIFIC EMBODIMENTS

One or more specific embodiments of the present invention will bedescribed below. In an effort to provide a concise description of theseembodiments, not all features of an actual implementation are describedin the specification. It should be appreciated that in the developmentof any such actual implementation, as in any engineering or designproject, numerous implementation-specific decisions must be made toachieve the developers' specific goals, such as compliance withsystem-related and business-related constraints, which may vary from oneimplementation to another. Moreover, it should be appreciated that sucha development effort might be complex and time consuming, but wouldnevertheless be a routine undertaking of design, fabrication, andmanufacture for those of ordinary skill having the benefit of thisdisclosure.

In accordance with the present technique, sensors for pulse oximetry orother applications utilizing spectrophotometry are provided that reducemotion artifacts by fixing the optical distance between an emitter and adetector when the sensor is applied to a patient. For example, in oneembodiment, a conformable sensor is provided that has a stiffeningmember adapted to hold the emitter and detector at a fixed opticaldistance when the sensor is applied to a patient. In another embodiment,an annular or partially annular sensor is provided that maintains afixed optical distance between an emitter and a detector when the sensoris applied to a patient's digit. Further, in an additional embodiment, aclip-style sensor is provided that holds the emitter and detector at afixed optical distance.

Motion artifacts in pulse oximetry are often generated by the movementof the pulse oximetry sensor relative to the optically probed tissue,which is typically caused by patient movement. Because pulse oximetry isoften used in settings where it is difficult to prevent patient motion,it is desirable to provide a mechanism for reducing the effects ofmotion on the pulse oximetry measurement. Generally, sensors arevulnerable to motion artifacts when the optical distance between asensor's emitter and detector varies due to an undesired mechanicalchange in the conformation of the sensor while in use.

A change in optical distance may include any change in position orgeometry of the emitter and/or the detector relative to the tissue orrelative to each other. More specifically, a change in optical distancemay involve a change in the path length, a change in the angle of theemitter or detector relative to one another, and/or a change in theangle of the emitter or detector relative to the tissue. For example, atapping or pressing motion by a patient may serve to compress a flexiblebandage sensor, decreasing the path length between the emitter anddetector. Alternatively, a tapping or pressing motion may partially opena clip-type sensor through pressure on the clip spring, thus increasingthe path length between the emitter and detector. For both a bandage anda clip-style sensor, a jerking or flexing motion may separate theemitter and detector, thus increasing the optical path length.Additionally, any of the above motions may twist or bend the sensor,causing the angle of the emitter and/or the detector to change relativeto the sensor and each other. As sensors do not typically emit nordetect light omnidirectionally; any motions that lead to variations inangle of sensor components may alter the amount of light detected, andmay force detected light through different portions of tissue. In anycase, variability in the optical path length due to motion can causemotion artifacts and obscure the desired pulse oximetry signal. Thus, itis desirable that a sensor's emitter and detector are held at asubstantially fixed optical distance with respect to one another.

By holding a sensor's emitter and detector at a substantially fixedoptical position with respect to one another, the sensors providedherein limit the modulations of detected light that may occur and theresulting measurement errors. These sensors substantially reduce theoccurrence of motion artifacts by reducing the change in position of thesensing components of the sensor with respect to each other and thetissue.

Keeping in mind the preceding points, the following exemplary sensordesigns are provided as examples of sensors that reduce motion artifactsby maintaining a fixed optical distance between an emitter and adetector of a sensor 10. It should be appreciated that a sensor 10according to the present teachings may be adapted for use on any digit,and may also be adapted for use on a forehead, earlobe, or other sensorsite. For example, a sensor 10 may be a clip-style sensor, appropriatefor a patient earlobe or digit. Alternatively, a sensor 10 may be abandage-style or wrap-style sensor for use on a digit or forehead.Alternatively, a sensor 10 may be an intrauterine sensor. Further, itshould be appreciated that a sensor 10 may also include adhesives tofacilitate securing of the sensing elements to the tissue. In certainembodiments, the adhesives may include an adhesive coating on thetissue-contacting surface of the sensor 10.

In accordance with some embodiments of the present technique, sensorsfor pulse oximetry or other applications utilizing spectrophotometry areprovided having a stiffening member to reduce variability in the opticaldistance between an emitter and a detector. For example, FIG. 1Aillustrates an exemplary transmission-type bandage sensor appropriatefor use on a patient digit. As shown in FIG. 1A, a sensor 10A may have astiffening member 12 that is applied to a conformable sensor body 14.The stiffening member 12 may be applied to a tissue-contacting surface16, adhesively or otherwise. As the stiffening member 12 may come intocontact with a patient's tissue, it may be generally constructed to haveno sharp edges in order to avoid patient discomfort. The stiffeningmember 12 may have windows or other openings (not shown) suitably sizedto accommodate an emitter 18 and a detector 20. The stiffening member 12may applied such that the windows or openings are in-line with theemitter and the detector to allow for normal light emitting andphotodetecting function. The sensor 10A may optionally include anoptically transparent adhesive layer 22 for affixing the sensor to thedigit. The adhesive layer 22 may be generally sized and shaped to coverthe tissue-contacting surface 16 of the conformable sensor body 22. Whenthe sensor 10A is applied to a patient's digit, the stiffening member isbent or otherwise shaped to conform to the digit. The sensor 10A isapplied such that the emitter 18 and the detector 20 lie on opposingside of the digit. After application of the sensor 10A, the emitter 18and the detector 20 are substantially resistant to movement relative toone another.

The stiffening member 12 (and stiffening members 36 and 42, below) maybe constructed from any suitable material that functions to hold theemitter and the detector of a sensor at a substantially fixed opticaldistance when the sensor 10A is applied to a patient. For example, asuitable stiffening member 12 may be metal, plastic or polymeric, orcardboard. In certain embodiments, suitable metals include aluminum orbrass. The stiffening member 12 may be in the shape of a strip, wire, ormesh that can be easily adapted for use with a conformable sensor body14. The stiffening member 12 may adapted to be easily bent, shaped,activated, or applied to a conformable sensor body 14 in order to holdan emitter and a detector at a substantially fixed optical distance. Thestiffening member 12 may be sized to substantially cover a majority ofthe tissue-contacting surface 16, or for reasons related to cost ortotal sensor weight, may be sized to form a strip that is generally inthe area surrounding the emitter 18 and the detector 20.

In certain embodiments, it may be advantageous to apply a stiffeningmember to a sensor surface that does not contact a patient's tissueduring normal use. For example, certain patients may be sensitive tometals, and thus in certain circumstances it may be desirable to limitthe amount of skin contact with a metal stiffening member. For thosepatients, a sensor 10B as shown in FIG. 2 may be appropriate. FIG. 2shows an embodiment of a sensor 10B in which a brass stiffening member24 is applied to a surface 26 that does not contact the tissue duringnormal use of the sensor 10B. The brass stiffening member 24 is appliedto the surface 26 along an imaginary axis connecting an emitter 28 and adetector 30. When the sensor 10B is applied to a patient's digit, thebrass stiffening member 24 is bent to conform to the digit withoutcoming in contact with the patient's tissue. In an alternate embodiment(not shown), the sensor 10B is adapted to operate in reflectance mode.The emitter 28 and detector 30 are positioned on the sensor body suchthat they lie side-by-side when applied to a patient's digit.

In certain embodiments, a stiffening member may be integrallyconstructed with the conformable sensor body, or may be a separatestructure. More specifically, in the embodiment shown in FIG. 3A, asensor 10C has a closed cavity 32 within the conformable sensor body 34into which a stiffening member 36 may be integrated or embedded.Alternatively, in certain embodiments, it may be advantageous to applythe stiffening member to the sensor at the time of use. FIG. 3Billustrates sensor 10D in which the conformable sensor body 38 has anopen cavity 40 that extends along the sensor body to provide an openinginto which a removable stiffening member 42 may be manually inserted atthe time of application of the sensor 10D to a patient. Before thesensor 10D is discarded after use, the removable stiffening member 42may be removed and stored for reuse. Having a removable stiffeningmember 42 that is reusable is not integral to the sensor 10D maydecrease sensor weight for shipping and transport, and thus may providecertain cost advantages.

In an alternate embodiment shown in FIG. 4A, a sensor 10E with anembedded stiffening member 44 within a closed cavity 46 in theconformable sensor body 48 may be adapted to operate in reflectancemode, such the emitter 50 and the detector 52 lie side-by-side when thesensor is applied to a patient. The stiffening member 44 includes arigid portion 45 disposed in the area adjacent to the emitter 50 and thedetector 52 and a more flexible portion 47. Thus, when the sensor 10E isapplied to a patient, the flexible portion 47 of the stiffening member44 allows the sensor 10E to be bent around a digit while addingstability to the conformable sensor body 48. The rigid portion 45surrounding the emitter 50 and the detector 52 may fix the geometry ofsensing elements, substantially reducing their ability to move relativeto one another. In an alternate embodiment, FIG. 4B illustratesreflectance sensor 10F in which the conformable sensor body 54 includesa rigid portion 57 that surrounds the emitter 60 and the detector 62.The rigid portion may be embedded in the sensor body 54, or may bedisposed on the tissue-contacting surface of the sensor body 54. FIG. 4Cillustrates an alternate embodiment of the sensor 10F in which theconformable sensor body 54 has an open cavity 56 that extends along thesensor body to provide an opening into which a flexible member 58 may bemanually inserted at the time of application of the sensor 10F to apatient. The rigid portion 57 is separate from the removable flexiblemember 58. Thus, if a healthcare worker feels that additional sensor 10Fstability may be advantageous, the flexible member 58 may be insertedinto the sensor 10F. When the sensor is applied to the patient, theemitter 60 and the detector 62 lie side-by-side on the same side of thetissue.

A stiffening member need not be solid, but may also be a fluid or othernon-solid material that stabilizes the optical distance between anemitter and a detector. In another embodiment, FIG. 5A shows a sensor10G in which the conformable sensor body 64 contains a bladder 66 thatis adapted to hold a fluid 68. The fluid 68 may be a liquid, gel, gas,or any suitable mixture thereof. It is contemplated that the stiffeningqualities of a gas or liquid may be realized by achieving a certainpressure in the bladder 66. Generally, it is contemplated that thebladder 66 should be fully inflated or mostly inflated with the fluid 68to hold the emitter 70 and the detector 72 at a fixed optical distance.In certain embodiments, a liquid or gel may harden after a period oftime. The fluid 66 described in the above embodiment may be any suitablefluid that acts to hold an emitter 70 and a detector 72 at asubstantially fixed optical distance when the sensor 10G is applied to apatient's digit. In certain embodiments, the fluid may be air or othergases and gas mixtures. In other embodiments, the fluid may be water.

In certain embodiments, it may be desirable employ a gas or gas mixturefor reasons related to cost, manufacturing convenience, and total sensorweight. In FIG. 5B, the sensor 10G is modified to include a valve 74 oranother suitable opening or gas injection site. The sensor may beapplied to a patient's digit when the valve 74 is in the closed positionand the bladder 66 is substantially empty and deflated. Afterapplication of the sensor 10G to the digit, the valve 74 is opened toallow air to flow into the bladder 66, which stiffens the sensor 10G tofix the distance between the emitter 70 and the detector 72. In otherembodiments, the valve 74 may be a fluid or epoxy injection site.

Another embodiment in which a fluid-containing stiffening member may beactivated upon application of the sensor to a patient is illustrated inFIG. 6. FIG. 6 depicts a sensor 10H with a first chamber 78 filled witha first material 80, and second chamber 82 filled with a second material84. A barrier 86 separates the first chamber 78 and second chamber 82.The barrier 86 is capable of being broken upon applying the sensor 82 toa patient. After the breaking of the barrier 86, the first material 80and the second material 84 will mix and form a composition that iscapable of hardening, thus stabilizing the optical distance between theemitter 88 and detector 90. For example, the first material 80 may becement or plaster, and the second material 84 may be water. In anotherembodiment, the first material 80 may be epoxy. In another embodiment,the first material 80 may be one part of a two-part epoxy in which afirst part of the epoxy, such as the base, is the first materials 80,and a second part of the epoxy, such as the catalyst or hardener, is thesecond material 84. Two part epoxies that may be used with a sensor 10Hinclude Loctite® 30680 (available from Henkel, Rocky Hill, Conn.),Blu-Mousse® (available from Parkell, Inc., Farmindale, N.Y.), LuxaCore®Smartmix dual from DMG (available from DMG, Englewood, N.J.), andExaflex (available from GC America, Inc., Alsip, Ill.).

In alternate embodiments, a stiffening member may be conditionallyactivated when exposed to air or light, placed in contact with skin,attached to the sensor site, conformed to fit to the sensor site,subjected to a specific environmental condition (e.g. when exposed tobody or room temperatures), subjected to a specific chemical reaction,programmed by software, or subjected to external force, (e.g., from thetissue being probed by the sensor). For example, a conditionallyactivated stiffening member may be a vacuum-packed polymer that forms arigid precipitate upon exposure to oxygen or water vapor. In otherembodiments, the stiffening member may include a light curing adhesivesuch as Loctite® Flashcure-4305 (available from Henkel, Rocky Hill,Conn.). In another embodiment, the stiffening member may include amaterial undergoes a chemical hardening, such a crystallization uponexposure to a crystal seed. One such material is supersaturated sodiumacetate solution that is exposed to a sodium acetate crystal. Othersuitable materials for forming conditionally activated stiffeningmembers include polyurethane and polystyrene foams that, for example,may expand and stiffen upon exposure to air.

FIG. 7 illustrates an alternate embodiment of the invention in which thestiffening member is a sleeve 92 that may be applied to a sensor,generically identified as a sensor 10, in order to mechanicallystabilize the distance between the emitter 94 and detector 96 afterapplication of the sensor 10. The sleeve 94 may have interior bumps orprotrusions such as foam bumpers 95, which serve to absorb shock andcushion the sensor 10 against external forces.

Although the previously discussed embodiments have described conformablesensors, it is also envisioned that similar advantages may be realizedby configuring relatively rigid sensors to hold an emitter and adetector at a fixed optical distance. For example, FIG. 8A shows a rigidannular sensor 10I adapted to be applied to a patient's digit. Thesensor 10I is adapted to be slid onto a patient digit, and may befurther secured by a bandage or adhesive. The rigidity of the sensor 10Iserves to hold the emitter 98 and the detector 100 at a fixed opticaldistance. In another embodiment (not shown), the sensor 10G may open ata hinge and also have a latch, snap, or other closing mechanism. Theannular sensor 10I may be adjusted with a strap 102, as shown in FIG.8B, or other adjustment mechanism in order to closely conform to thedigit.

FIG. 9 shows a partially annular sensor 10J that may be placed on adigit and self-secured or secured by a bandage or other means. Thesensor 10J is generally at least hemi-annular in order to providesufficient grip on the digit. An emitter 104 and a detector 106 arearranged such that, when the sensor is applied to the digit, they wouldbe on opposite sides of the digit.

The annular or partially annular sensors (e.g. sensors 10I and 10J) maybe constructed from plastic, metal, cardboard, or any other suitableresilient material. It is contemplated the sensors 10I and 10J may besized to approximately correlate to the profile of a jewelry ring.Alternatively, the sensors 10I and 10J may be sized to approximatelycorrelate to the size of the first finger joint, such that when a sensor10I or 10J is applied to the digit, the fingernail region of a digit isgenerally covered by the sensor, but the sensor does not interfere withflexing or bending of the finger joint.

In another embodiment, a reusable clip-style sensor adapted for use oneither a digit or an earlobe is provided that holds an emitter anddetector at a fixed optical distance with the use of a spacer. Such asensor adapted for use on a patient earlobe is shown in FIG. 10, whichillustrates a sensor 10K having a first portion 108 and a second portion110 that may be moved towards one another or away from one another. Thefirst portion 108 and the second portion 110 are each able to engage aspacer 112 that is controlled by a threaded pin 114. The spacer 112controls the distance between the first portion 88 and the secondportion 110 as the threaded pin 114 moves the spacer 112 along an angledtrack. The first portion 108 has an emitter 116 disposed on thetissue-contacting surface and the second portion 110 has a detector 118disposed on the tissue-contacting surface. When the sensor 10K isapplied an earlobe, the spacer 112 may be adjusted such that the sensor10K provides a desired amount of tension to the earlobe whilemaintaining a fixed optical distance between the first portion 108 andthe second portion 110.

An alternate embodiment of a clip-style sensor 10L with a spacer isdepicted in FIG. 11A. As shown, a first portion 120 and a second portion122 of the sensor 10L may be fixed in place after application to anearlobe with a removable spacer 124. The removable spacer 124 slidesinto a space 106 between the first portion 120 and the second portion122 and prevents the first portion 120 and the second portion 122 frommoving relative to one another. As shown in FIG. 11B, the removablespacer has grooves 128 and 130 into which suitably sized regions of thefirst portion 120 and the second portion 122 may slide. When the firstportion 120 and the second portion 122 are fixed in grooves 128 and 130,they are unable to move relative to one another. The removable spacer124 is shown with an angled profile, but may be shaped or sized in anysuitable configuration that serves to hold the first portion 120 and thesecond portion 122 at a fixed optical distance when the spacer 124 isengaged. The removable spacer 124 may be further fixed in placemagnetically (not shown).

Alternatively, in FIG. 12, a sensor 10M is illustrated in which thedistance between a first portion 132 and a second portion 134 of theclip-style sensor 10M is controlled by a sliding pin 136. The slidingpin 136 and the first portion 132 and the second portion 114 arepartially enclosed within a housing 137. The first portion 132 and thesecond portion 134 have attachment slots 138 that are able to engage thesliding pin 136. Thus, when the sliding pin 136 is pulled, the firstportion 132 and the second portion 134 move towards one another. Whenthe sliding pin 136 is pushed, the first portion 132 and the secondportion 134 move away from one another. The first portion 132 and thesecond portion 134 may be adapted to house an emitter and a detector(not shown). To apply the sensor 10M to the patient, the sliding pin 136is pushed into the housing 137 to increase the distance between thefirst portion 132 and the second portion 134 in order to accommodate thepatient's tissue. The sliding pin 136 may then be pushed into thehousing 137 until the desired pressure from the sensor 10M on thepatient's tissue is reached.

A sensor, illustrated generically as a sensor 10, may be used inconjunction with a pulse oximetry monitor 140, as illustrated in FIG.13. It should be appreciated that the cable 142 of the sensor 10 may becoupled to the monitor 140 or it may be coupled to a transmission device(not shown) to facilitate wireless transmission between the sensor 10and the monitor 140. The monitor 140 may be any suitable pulse oximeter,such as those available from Nellcor Puritan Bennett Inc. Furthermore,to upgrade conventional pulse oximetry provided by the monitor 140 toprovide additional functions, the monitor 140 may be coupled to amulti-parameter patient monitor 144 via a cable 146 connected to asensor input port or via a cable 148 connected to a digitalcommunication port.

The sensor 10 includes an emitter 150 and a detector 152 that may be ofany suitable type. For example, the emitter 150 may be one or more lightemitting diodes adapted to transmit one or more wavelengths of light inthe red to infrared range, and the detector 152 may one or morephotodetectors selected to receive light in the range or ranges emittedfrom the emitter 150. Alternatively, an emitter 150 may also be a laserdiode or a vertical cavity surface emitting laser (VCSEL). An emitter150 and detector 152 may also include optical fiber sensing elements. Anemitter 150 may include a broadband or “white light” source, in whichcase the detector could include any of a variety of elements forselecting specific wavelengths, such as reflective or refractiveelements or interferometers. These kinds of emitters and/or detectorswould typically be coupled to the rigid or rigidified sensor via fiberoptics. Alternatively, a sensor 10 may sense light detected from thetissue is at a different wavelength from the light emitted into thetissue. Such sensors may be adapted to sense fluorescence,phosphorescence, Raman scattering, Rayleigh scattering and multi-photonevents or photoacoustic effects. For pulse oximetry applications usingeither transmission or reflectance type sensors the oxygen saturation ofthe patient's arterial blood may be determined using two or morewavelengths of light, most commonly red and near infrared wavelengths.Similarly, in other applications, a tissue water fraction (or other bodyfluid related metric) or a concentration of one or more biochemicalcomponents in an aqueous environment may be measured using two or morewavelengths of light, most commonly near infrared wavelengths betweenabout 1,000 nm to about 2,500 nm. It should be understood that, as usedherein, the term “light” may refer to one or more of ultrasound, radio,microwave, millimeter wave, infrared, visible, ultraviolet, gamma ray orX-ray electromagnetic radiation, and may also include any wavelengthwithin the radio, microwave, infrared, visible, ultraviolet, or X-rayspectra.

The emitter 150 and the detector 152 may be disposed on a sensor body154, which may be made of any suitable material, such as plastic, foam,woven material, or paper. Alternatively, the emitter 150 and thedetector 152 may be remotely located and optically coupled to the sensor10 using optical fibers. In the depicted embodiments, the sensor 10 iscoupled to a cable 142 that is responsible for transmitting electricaland/or optical signals to and from the emitter 150 and detector 152 ofthe sensor 10. The cable 142 may be permanently coupled to the sensor10, or it may be removably coupled to the sensor 10—the latteralternative being more useful and cost efficient in situations where thesensor 10 is disposable.

The sensor 10 may be a “transmission type” sensor. Transmission typesensors include an emitter 150 and detector 152 that are typicallyplaced on opposing sides of the sensor site. If the sensor site is afingertip, for example, the sensor 10 is positioned over the patient'sfingertip such that the emitter 150 and detector 152 lie on either sideof the patient's nail bed. In other words, the sensor 10 is positionedso that the emitter 150 is located on the patient's fingernail and thedetector 152 is located 180° opposite the emitter 150 on the patient'sfinger pad. During operation, the emitter 150 shines one or morewavelengths of light through the patient's fingertip and the lightreceived by the detector 152 is processed to determine variousphysiological characteristics of the patient. In each of the embodimentsdiscussed herein, it should be understood that the locations of theemitter 150 and the detector 152 may be exchanged. For example, thedetector 152 may be located at the top of the finger and the emitter 150may be located underneath the finger. In either arrangement, the sensor10 will perform in substantially the same manner.

Reflectance type sensors also operate by emitting light into the tissueand detecting the light that is transmitted and scattered by the tissue.However, reflectance type sensors include an emitter 150 and detector152 that are typically placed on the same side of the sensor site. Forexample, a reflectance type sensor may be placed on a patient'sfingertip or forehead such that the emitter 150 and detector 152 lieside-by-side. Reflectance type sensors detect light photons that arescattered back to the detector 152. A sensor 10 may also be a“transflectance” sensor, such as a sensor that may subtend a portion ofa baby's heel.

While the invention may be susceptible to various modifications andalternative forms, specific embodiments have been shown by way ofexample in the drawings and have been described in detail herein.However, it should be understood that the invention is not intended tobe limited to the particular forms disclosed. Indeed, the presenttechniques may not only be applied to measurements of blood oxygensaturation, but these techniques may also be utilized for themeasurement and/or analysis of other blood and/or tissue constituentsusing principles of pulse oximetry. For example, using the same,different, or additional wavelengths, the present techniques may beutilized for the measurement and/or analysis of carboxyhemoglobin,methemoglobin, total hemoglobin, fractional hemoglobin, intravasculardyes, and/or water content. Rather, the invention is to cover allmodifications, equivalents, and alternatives falling within the spiritand scope of the invention as defined by the following appended claims.

1. A sensor comprising: a conformable sensor body; a removablestiffening member disposed within an open cavity in the sensor body; andan emitter and a detector disposed on the stiffening member, wherein theemitter and the detector are adapted to operate in reflectance mode, andwherein the sensor body is adapted to hold the emitter and detector at asubstantially fixed optical distance relative to one another when thesensor is applied to a patient.
 2. The sensor, as set forth in claim 1,wherein the sensor comprises at least one of a blood constituent sensoror a tissue constituent sensor.
 3. The sensor, as set forth in claim 1,wherein the sensor comprises at least one of a pulse oximetry sensor ora sensor for measuring a water fraction.
 4. The sensor, as set forth inclaim 1, wherein the sensor comprises at least one of acarboxyhemoglobin sensor or a methemoglobin sensor.
 5. The sensor, asset forth in claim 1, wherein the sensor is adapted for intrauterineuse.
 6. The sensor, as set forth in claim 1, wherein the stiffeningmember is embedded within the sensor body.
 7. The sensor, as set forthin claim 1, wherein the stiffening member comprises a metal or a rigidpolymeric material.
 8. A pulse oximetry system comprising: a pulseoximetry monitor; and a pulse oximetry sensor adapted to be operativelycoupled to the monitor, the sensor comprising: a conformable sensorbody; a removable stiffening member disposed within an open cavity inthe sensor body; and an emitter and a detector disposed on thestiffening member, wherein the emitter and the detector are adapted tooperate in reflectance mode, and wherein the sensor body is adapted tohold the emitter and detector at a substantially fixed optical distancerelative to one another when the sensor is applied to a patient.
 9. Thesystem, as set forth in claim 8, wherein the sensor comprises a tissueconstituent sensor.
 10. The system, as set forth in claim 8, wherein thesensor comprises a sensor for measuring a water fraction.
 11. Thesystem, as set forth in claim 8, wherein the sensor comprises at leastone of a carboxyhemoglobin sensor or a methemoglobin sensor.
 12. Thesystem, as set forth in claim 8, wherein the sensor is adapted forintrauterine use.
 13. The system, as set forth in claim 8, wherein thestiffening member is embedded within the sensor body.
 14. The system, asset forth in claim 8, wherein the stiffening member comprises a metal ora rigid polymeric material.
 15. A method of manufacturing a pulseoximetry sensor, comprising: providing a conformable sensor body adaptedfor use on a patient's digit; providing a removable stiffening memberdisposed within an open cavity in the sensor body; and providing anemitter and a detector disposed on the stiffening member, wherein theemitter and the detector are adapted to operate in reflectance mode, andwherein the sensor body is adapted to hold the emitter and detector at asubstantially fixed optical distance relative to one another when thesensor is applied to a patient.
 16. The method, as set forth in claim15, wherein the sensor comprises at least one of a blood constituentsensor or a tissue constituent sensor.
 17. The method, as set forth inclaim 15, wherein the sensor comprises at least one of a pulse oximetrysensor or a sensor for measuring a water fraction.
 18. The method, asset forth in claim 15, wherein the sensor comprises at least one of acarboxyhemoglobin sensor or a methemoglobin sensor.
 19. The method, asset forth in claim 15, wherein the stiffening member is embedded withinthe sensor body.